1. Field of the Invention
The present invention relates to an electric discharge machine for processing a workpiece by means of an electric discharge arc generated between an electrode and the workpiece.
2. Description of the Related Art
FIG. 4 shows the construction of a conventional electric discharge machine. A first rotary device 4 is disposed in a processing cell 1 filled with a processing solution 2. A workpiece 3 to be processed is attached to a rotary shaft 4a of the rotary device 4. On the other hand, a second rotary device 7 attached to the end of a spindle 8 is disposed above the processing cell 1. An electrode 5 is attached to a rotary shaft 7a of the rotary device 7. The electrode 5 is disposed to oppose the portion of the workpiece 3 to be processed, within the processing solution 2. A cutting jig 9 is disposed in the processing cell 1 through the intermediary of an insulation bed 10. The cutting tool 9 is electrically insulated from the processing cell 1 by the insulation bed 10.
In operation, the spindle 8 is moved horizontally so that the electrode 5 is moved closer to the portion of the workpiece 3 to be processed. In this state, the first and second rotary devices 4 and 7 are operated to cause the workpiece 3 and the electrode 5 to rotate about the axes of the rotary shafts 4a and 7a and a voltage is applied between the workpiece 3 and the electrode 5 by means of a power supply device (not shown) so as to cause an electrical discharge therebetween, whereby the workpiece 3 is processed into a shape corresponding to the shape of the electrode 5.
As shown in FIG. 5, the end of the electrode 5 is progressively consumed as a result of the electrical discharge. If the processing is continued, it becomes impossible to obtain the desired shape of the workpiece 3 because of excessive consumption D of the electrode 5. Therefore, the processing is temporarily stopped and the spindle 8 is moved towards the cutting tool 9. The cutting tool 9 then cuts the electrode 5 to recover the initial shape of the electrode 5. Subsequently, the spindle 8 is moved again towards the workpiece 3 and the processing by electrical discharge is again commenced. The cutting of the electrode 5 is conducted occasionally as required until one cycle of electrical discharge processing is completed.
Thus, the conventional electric discharge machine has suffered from a problem in that the processing efficiency is seriously impaired because the discharge has to be suspended to enable cutting of the electrode 5 which is worn during the processing by electric discharge.